1. Field of the Invention
This invention pertains to a system for the underground receipt and storage of liquid product, such as distilled petroleum products, e.g., gasoline. More specifically, it pertains to a system designed to connect an underground storage tank with an above-ground dispensing means, whereby all potential leaks in the system will be entrapped in a secondary containment and returned to a recovery tank, from which the product can be monitored or used.
2. Background of the Prior Art
Many liquid products are stored, for varying periods of time, in underground storage tanks and the like. A principal, but by no means limiting, example of such liquid is gasoline, along with other petroleum distillates. For dispensing at a service station, these products are generally loaded into an underground storage tank, from a tank truck or similar means, through a hose connecting the two. The product is dispensed from the storage tank to an above-ground dispensing means, usually with the aid of a submersible pump.
In recent years, increasing attention has been directed to the potential for environmental problems presented by such tanks and systems. Among the problems identified is the corrosion of the tank, and related materials, itself, generally presented by tanks constructed of steel materials, and similar corrosion-susceptible alloys. Thus, as discussed in U.S. Pat. Nos. 3,335,904 and 3,700,512, tanks comprised of corrosion-resistant material, which exhibits satisfactory stiffness and strength requirements, are increasingly adopted. One material widely used is fiberglass reinforced resinous material, for example, isophthalic resins.
While such tanks may be corrosion resistant, the possibility for leakage through the wall of the tank persists. Accordingly, certain jurisdictions have adopted regulations requiring the use of double walled tanks, such as that described in U.S. Pat. No. 4,676,093. A similar double-wall tank, comprised of steel, is disclosed in U.S. Pat. No. 1,886,074. In such double walled tanks, the annular space between the walls is generally occupied by a monitoring means of some sort, either a liquid, the level of which falls upon the development of a leak in either the inner or the outer tank, or a monitor, provided at the bottom of the tank, when installed, which will detect the presence of petroleum products thereat.
However, while considerable attention has been devoted to designing appropriate double-walled tanks of corrosion-resistant materials to reduce the potential for environmental hazard, relatively little attention has been paid to the commercial loss of product due to leakage in the system which places the storage tank in communication with the above-ground dispensing device, and the environmental hazard posed thereby. One attempt to address these problems is described in U.S. Pat. No. 4,639,164. Therein, "sumps" are provided on inlet and outlet fittings on the storage tank, which sumps are intended to catch or retain leakage at the fittings to the tank. However, the system fails to retain the material in such a fashion that it may be reused, cannot be used to monitor the amount and rate of leakage, and, to remove the leakage from the sump, requires a pump in an above ground holding tank. Moreover, the system described in U.S. Pat. No. 4,639,164, does not provide for, or describe, the means by which attachments to conventional equipment, such as submersible pumps, fill pipes and the like, may be made, and maintain the integrity of the system.
Accordingly, it remains an object of this technology to provide a complete system design for underground installation, for the containment and delivery of liquid product from an underground storage tank to an above-ground dispensing device, including means for filling the tank, and delivering the fuel to the dispensing means.